The primary goal of this application is to use a combination of acoustic and behavioral responses to test theories of auditory processing at the mechanical and behavioral levels. A subordinate goal is to relate acoustic responses measured non-invasively in the ear canal to cochlear and middle ear function. The first aim studies the relationships between middle ear and cochlear mechanics using a combination of experimental and theoretical approaches. Measurements of stimulus-frequency otoacoustic emission (SFOAE) and otoreflectance measurements will be used to predict hearing loss, an improved test of acoustic reflex function will be used to study middle-ear noise sources and no linearity, and time-domain models of middle-ear and cochlear energy transmission will be developed and evaluated based on experimental measurements performed in this application or reported in the literature. The second aim studies the effects of cochlear no linearity on spectral processing using SFOAE stimulus conditions similar to those used in behavioral experiments on simultaneous and non-simultaneous masking and suppression. Specifically, the experiments will address the extent to which SFOAE measurements of peripheral mechanics are able to noninvasive assess the strength of the medial olive-cochlear (MOC) efferent system on outer hair cell function, assess the level dependence of SFOAE fine structure, and account for the performance of normal-hearing listeners and listeners with sensor neural hearing loss in detecting tones in broadband and notched noise. The third aim studies the effects of cochlear no linearity on temporal processing using SFOAE stimulus conditions similar to those used in behavioral experiments on overshoot and amplitude modulation (AM). These experiments will assess the shifts in SFOAEs produced by activation of the MOC system in response to sounds with AM, and will test the extent to which SFOAE measurements can account for measurements of behavioral overshoot in normal listeners and subjects with auditory neuropathy. The results of the proposed experiments will provide useful data and modeling to improve our understanding of the auditory periphery in humans, and may improve our ability to diagnose the magnitude of hearing loss and improve our understanding of the impact of hearing loss on spectral and temporal resolution.